Pile cutters for tufting machines have been known from various prior-art embodiments. For example, document U.S. Pat. No. 2,090,021 discloses a pile cutter with a gripper finger being provided on its underside with a cutting edge having two steps. Furthermore, a cutting knife arranged in the pile cutter is disposed for cutting the open the taken up loops in a targeted manner in order to produce cut pile.
Furthermore, document EP 0 200 810 A1 shows a pile cutter having a hard-metal inlay that defines a cutting edge offset upward relative to the lower edge of the pile cutter. Adjoining the cutting edge, there is a step on which extends a straight edge up to the free end of the pile cutter. A leaf spring is movably arranged on the pile cutter in longitudinal direction of the gripper finger. By sliding the leaf spring forward or retracting it, the cutter can be switched from one operating mode in which the loop pile is produced into another operating mode in which the cut pile is produced.
Knives moving next to the grippers are used in the production of cut pile in most cases. A problem occurring here is the asymmetrical cut. The loops grasped by the pile cutter tend to be cut open not precisely on their vertex but slightly to the side, thus resulting in a not fully uniform pile height. In order to eliminate this problem, document EP 1 953 290 A1 has suggested that a lateral recess be provided on the pile cutter. On the other side of the pile cutter there is provided a flat hard metal inlay that supports the cutting edge. Due to the recess, the pile cutter is particularly narrow at the cutting edge, so that taken up loops are cut at least approaching their vertex.
Still, problems may result when the loops consist of particularly slippery material. If these are shifted in longitudinal direction of the cutting edge before or during the cutting operation, the loop may draw, and the cut may not be clean or, again, be off-center.
In order to prevent a slipping of the loops on a pile cutter, document EP 76783 B1 suggests that a serrated cutting edge be formed on a pile cutter for cut pile. This serration of the cutting edge prevents a slipping of the taken up loops in longitudinal direction of the pile cutter.
Furthermore, document U.S. Pat. No. 1,907,292 discloses a pile cutter with a toothed cutting edge.
In addition, document U.S. Pat. No. 2,842,080 discloses a pile cutter with a stepped cutting edge for the production of various pile heights.
In the production of cut pile using particularly slidable, however cutting-resistant, pile thread the latter tends to evade ahead of the cutting knife. Therefore, during the cutting operation, the thread may be shifted along the cutting edge and be ultimately partially cut or cut all the way through due to the increasing tension on the cutting edge, while the cut is not guided cleanly by the knife. This is true, in particular, for materials that slide easily but, at the same time, are not easy to cut such as, e.g., certain synthetics, for example polyester threads, or coated threads that are used in the production of dirt-repellant carpeting.